by Kris Osborn, Warrior As the world’s attention fixates on the high volume of fast-arriving 5th-and-6th-Generation stealth fighters in places such as the U.S. China and Russia, there is a less visible effort to ensure the value of upgraded 4th-generation aircraft is not fully dismissed or forgotten. This is perhaps best evidenced through the growing arrival of the 4.5-gen F-15EX aircraft, a massively modernized and upgraded F-15 aircraft intended to help bring [https://www.ainonline.com/aviation-news/defense/2026-02-03/south-korea-opts-upgrade-slam-eagles] advanced “mass” air attack in support of 5th-generation stealth jets. The Republic of Korea is one of the most recent countries to lend support to the continued combat-value of non-stealthy F-15EX aircraft, as it is now upgrading its F-15K “Slam Eagle” fleet to align with the kinds of technologies woven into the F-15EX. South Korea is already an F-35 country, so some might question the wisdom of adding upgraded 4th-gen aircraft such as F-15EX kinds of lethality and survivability upgrades. [https://www.stripes.com/branches/air_force/2025-12-19/cockpit-displays-f15ex-fighters-20141970.html] Hypersonic F-15EX As for its many attributes [https://www.defensenews.com/global/asia-pacific/2024/11/21/the-f-15-fighter-jet-is-having-a-second-spring-in-asia/], the F-15EX may reportedly fire hypersonic weapons, hit speeds of Mach 2.5 and operate with one of the fastest computer processors ever to exist in combat aircraft. Therefore, the actual extent to which the F-15EX could actually rival or challenge the Chinese J-20 or Russian Su-57 may not be fully known, it does appear possible the new “4th-gen-plus” aircraft might be well positioned to destroy Russian and Chinese 4th generation fighters, of which there are many. While considered a massively upgraded fourth-Gen aircraft balancing itself on an interesting boundary between 4th-and 5th-gen aircraft, the F-15EX is of course slightly less stealthy than full 5th-Gen platforms such as the F-22 and F-35. However, there are a number of not-yet-seen innovations built into the F-15EX with the aim of making it an impactful asset should it be needed for major power warfare. There are many elements to this, based in large measure on the broad recognition that the 1980s-era aircraft is, essentially, an entirely different jet that it was decades ago. Elements of the basic airframe structure are similar, however the F-15EX is now engineered with a new generation of technologies intended to reshape its tactical significance when it comes to high-end warfare. Many of the innovations woven into the F-15EX also build upon previous upgrade efforts taken up by Boeing to extend the aircraft into the 2040s and beyond. [https://aerospaceglobalnews.com/news/south-korea-f-15k-upgrade/] AESA F-15 The technological enhancements [https://www.airandspaceforces.com/f-15ex-jets-deploy-to-kadena-training-mission-prepare-for-transition-new-fighters/] built into the F-15EX arguably make it much more effective than any existing 4th-generation aircraft as it is engineered with a new suite of electronic warfare, AESA(Active Electronically Scanned Array) radar, high-speed computer processing and even an ability to fire new generation weapons.The thinking, as explained by developers, is to engineer a highly capable aircraft able to pick up key high-risk missions that may not necessarily require a 5th- or 6th-generation plane. Some have questioned the wisdom of building a non-stealthy F-15EX, given that major adversaries are likely to soon operate with threatening levels of 5th-generation stealth aircraft.It may not be fully clear just how many J-20s the Chinese will have in the future, and Russia is now building a relatively small number of Su-57s thus far. The 5th-generation air threat posed by both Russia and China is quite significant as something that arguably may require the U.S. and its allies to “mass” larger formations of networking F-35s and n [https://defence-industry.eu/boeing-clinches-2-8-billion-deal-to-modernize-and-upgrade-south-koreas-f-15k-slam-eagle-fighters/]ew 6th-generation aircraft. In recent years, Boeing developers have said that the F-15EXs Advanced Display Corps Processor [https://www.af.mil/News/Article-Display/Article/849185/f-15s-new-advanced-high-speed-mission-computer-makes-first-flight/] performs 87-billion computing functions per second. This and other F-15EX attributes, however, may not compensate for a clear lack of stealth. Non-Stealthy F-15 The lack of stealth suggests [https://en.yna.co.kr/view/AEN20251218002400320] that the F-15EX could indeed be quite vulnerable to now highly advanced Russian and Chinese air defenses. Russian S-400 and S-500 air-defense systems are claimed by the Russian press to operate with an ability to find and destroy stealth aircraft. This may or may not actually be true, as establishing an “engagement” track on 5th-generation stealth fighters is much harder than simply “detecting” that something is in the area. However, Russian air defenses, and possibly Chinese HQ-9s, are believed to operate on a wider range of frequencies, detect aircraft at higher altitudes and use digital networking and processing to connect otherwise disparate threat detection nodes to one another. If an F-15EX had the long range sensors, varied guidance systems, advanced computing, threat library identification data and vastly improved weapons reach, could it destroy enemy air defenses or 5th-Gen platforms without having to engage itself in close proximity? Should an F-15EX operate with the sensing, AI-enabled computing, threat identification and radar technology and long-range weapons guidance systems in any way comparable to existing 5th-Gen aircraft, then there certainly may be an argument for deploying the F-15EX in a major power warfare scenario amid an attack campaign aimed at establishing air superiority against an advanced rival. After all, part of the rationale for F-35 superiority is based upon the notion that it is designed to find and kill multiple enemy aircraft, and air defenses, before it is itself even seen. Could this be possible for a non-stealthy F-15EX Eagle II? Perhaps. Yet arguably not at the same time, as stealth is considered by many to be an indispensable attribute when it comes to countering advanced air defenses. This may be the thinking on the part of advocates, however many 5th-Gen advocates are likely to insist that only a true, stealthy 5th-Gen aircraft could succeed in those kinds of advanced, ultrahigh-threat great power war scenarios. Some have gone so far as to suggest that an advanced 4th-Gen aircraft might linger in a kind of liminal zone, meaning it may be far too advanced for counterinsurgency, yet not capable of engaging the most high-end great power threats Kris Osborn is the President of Warrior Maven – Center for Military Modernization. Osborn previously served at the Pentagon as a highly qualified expert in the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel. He also has a Masters Degree in Comparative Literature from Columbia University
